Behavior Of Electrodes Research Articles

Statistics design for the synthesis optimization of lignin-sulfonate sulfur-doped mesoporous carbon materials: promising candidates as adsorbents and supercapacitors materials

This study employed lignin-sulfonated (LS) to develop biobased carbon materials (LS-Cs) through a sulfur-doping approach to enhance their physicochemical properties, adsorption capabilities, and energy storage potentials. Various characterization techniques, including BET surface area analysis, SEM imaging, XPS, Raman spectroscopy, and elemental composition (CHNS), were employed to assess the quality of the LS-Cs adsorbent and electrode samples. Response Surface Methodology (RSM) was utilized for optimizing the two main properties (specific surface area, ABET, and mesopore area, AMESO) by evaluating three independent factors (i.e., activation temperature, ZnCl2:LS ratio, and sulfur content). According to the statistical analysis, ABET and AMESO were affected by ZnCl2 and sulfur content, while the pyrolysis temperature did not affect the responses in the studied conditions. It was found that increasing the ZnCl2 and sulfur contents led to an increment of the ABET and AMESO values. The LS-C materials exhibited very high ABETvalues up to 1993 m2 g−1 and with predominantly mesoporous features. The S-doping resulted in LS-Cs with high sulfur contents in their microstructures up to 15% (wt%). The LS-C materials were tested as adsorbents for sodium diclofenac (DCF) adsorption and reactive orange 16 dye (RO-16) and as electrodes for supercapacitors. The LS-Cs exhibited excellent adsorption capacity values for both molecules (197–372 mg g−1) for DCF, and (223–466 mg g−1) for RO-16. When tested as electrodes for supercapacitors, notably, LS-C3, which is a doped sample with sulfur, exhibited the best electrochemical performance, e.g. high specific capacitance (156 F/g at 50 mV/s), and delivered an excellent capacitance after 1000 cycles (63 F/g at 1 A/g), which denotes the noteworthy capacitive behavior of the S-doped electrode. Thus, the present work suggests an eco-friendly resource for developing effective, productive carbon materials for adsorbent and electrodes for SC application. However, further studies on the complete application of these materials as adsorbents and electrodes are needed for a deeper understanding of their behavior in environmental and energy storage applications.

Toward the Rechargeable Aqueous Zinc Ion Batteries with Improved Overall Performance: Electrolyte with Surface Adsorptive Additive.

Aqueous zinc-ion batteries (AZIBs) with slightly acidic electrolytes process advantages such as high safety, competitive cost, and satisfactory electrochemical performance. However, the failure behaviors of both electrodes, regarding zinc dendrite growth, interfacial parasitic reactions, and the collapse of cathode materials hinder the practical application of ZIBs. To alleviate the issues of both anode and cathode at the same time, D-xylose (DX) is introduced to the electrolyte as a multifunctional additive. As a result, the side reaction of the anode is suppressed and the metallic deposition behavior is regulated due to the hydrogen bonding network reconstruction and preferential surface adsorption of DX; for the MnO2 cathode, the DX adsorption can help the interfacial charge transfer and increase the reactive sites. Benefiting from these merits, DX-optimized Zn//Zn battery displays reveal a prolonged lifespan of 6912h and an ultra-high cumulative capacity of 17.28Ahcm-2 at 5mAcm-2. With the function of water reactivity suppression, the Coulombic efficiency reaches 99.91% at 2mAcm-2; the Zn||MnO2 full batteries exhibit excellent cyclability over 2000 cycles at 5C with an increased capacity of 118.9mAhg-1, indicating the dual functions to both of the electrodes for AZIBs.

Porous silicon/carbon composites as anodes for high-performance lithium-ion batteries

Silicon anodes are promising for use in lithium-ion batteries. However, their practical application is severely limited by their large volume expansion leading to irreversible material fracture and electrical disconnects. This study proposes a new top-down strategy for preparing microsize porous silicon and introduces polyacrylonitrile (PAN) for a nitrogen-doped carbon coating, which is designed to maintain the internal pore volume and lower the expansion of the anode during lithiation and delithiation. We then explore the effect of temperature on the evolution of the structure of PAN and the electrochemical behavior of the composite electrode. After treatment at 400 -, the PAN coating retains a high nitrogen content of 11.35%, confirming the presence of C―N and C―O bonds that improve the ionic-electronic transport properties. This treatment not only results in a more intact carbon layer structure, but also introduces carbon defects, and produces a material that has remarkable stable cycling even at high rates. When cycled at 4 A g−1, the anode had a specific capacity of 857.6 mAh g−1 even after 200 cycles, demonstrating great potential for high-capacity energy storage applications.

Efficient sensitive detection of nitrite with Binary Y/Fe-modified multiwalled carbon nanotube nanocomposite by electrochemical approaches

Low-dimensional metal nanoparticles (MNPs) intercalated with three-dimensional multiwalled carbon nanotube (MWCNT) materials may be combined to produce new nanocomposites for enhancing their chemical, structural, and morphological features. These composites have interesting physical and chemical characteristics that can be used in electrochemical sensing systems that work significantly well. This research presents a new method for detecting nitrite using an electrochemical sensor that utilizes a flat-electrode made of GCE fabricated by nanocomposite of MWCNTs intercalated with yttrium oxide (Y2O3) and iron oxide (Fe2O3) as Y/Fe-MWCNT at higher temperature. FT-IR, UV–vis., SEM, powder XRD, EDS, BET, and TEM were significantly used to characterize in detail the nanocomposite after its preparation by the solid-state chemical approach. Using CV, LSV, and EIS techniques, the electrochemical attributes of both the bare and Y/Fe-MWCNT fabricated electrodes (with the help of 5 % Nafion as conducting coating binder) were investigated. In addition, the linear relationship between nitrite concentration and peak current of LSV was seen between 1.0 and 1.6 M, with a lower limit of detection (LOD) of 0.027 M. When compared to modified electrodes with nitrite, the electrocatalytic behavior of the nanocomposite electrode is enhanced significantly. At applied potential window of −0.1 to +1.8 V, the Y/Fe-MWCNT sensor shows good selectivity even when there are a lot of interfering chemicals and metal ions. In addition, different PBS electrolyte solutions with pH values ranging from 6.5 to 8 were used to study the prepared sensor. The standard addition method was employed to detect the unidentified nitrite concentration in various real samples including sea water, industrial wastewater, and well water. It introduced a new route for the development of noble sensor probe with nanocomposite materials by electrochemical approach for the safety of environmental and health care field in a broad scale.

Live Cell Imaging Studies on Orange Emitting Thiazole-Pyridone Azo Fluorophore and Its Latent Fingerprints, Computational, Electrochemical Sensing for Dopamine Detection.

The fluorescent materials have sparked a lot of research interests due to their unique electronic, optical and chemical characteristics. Here, we are intended to present a simple and facile synthesis of novel orange emitting thiazole-pyridone fluorescent tag (TPFT) by a simple diazo coupling reaction and the structural elucidation was carried out by IR, NMR (1H and 13C), UV-Vis, photoluminescence and HR-MS spectrometry. The solvatochromic behaviour of the TPFT offered crucial information about the formation of hydrazone and azo tautomeric forms. The DFT simulations are computed to calculate HOMO-LUMO energy gap (3.028 eV) of TPFT along with MEP and RDG analyses. Comprehensive LFP visualization is revealed under both normal and UV light conditions (365 nm). The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to analyse the electrochemical behaviour of the TPFT-modified glassy carbon electrode (MGCE) and exhibited a lower detection limit of 7.89 × 10-8 M (S/N = 3) with a linear range of 0.5-8.0 μM for DA detection. The live-cell imaging study of TPFT showed a strong blue emission at 453 nm, which generally indicates the existence of fluorescence stability.

Pomegranate Peel-Derived Hard Carbons as Anode Materials for Sodium-Ion Batteries.

Exploring high-performance carbon anodes that are low-cost and easily accessible is the key to the commercialization of sodium-ion batteries. Producing carbon materials from bio by-products is an intriguing strategy for sodium-ion battery anode manufacture and for high-value utilization of biomass. Herein, a novel hard carbon (PPHC) was prepared via a facile pyrolysis process followed by acid treatment using biowaste pomegranate peel as the precursor. The morphology and structure of the PPHC were influenced by the carbonization temperature, as evidenced by physicochemical characterization. The PPHC pyrolyzed at 1100 °C showed expanded interlayer spacing and appropriate oxygen group content. When used as a sodium ion battery anode, the PPHC-1100 demonstrated a reversible capacity of up to 330 mAh g-1, maintaining 174 mAh g-1 at an increased current rate of 1 C. After 200 cycles at 0.5 C, the capacity delivered by PPHC-1100 was 175 mAh g-1. The electrochemical behavior of PPHC electrodes was investigated, revealing that the PPHC-1100 possessed increased capacitive-controlled energy storage and improved ion transport properties, which explained its excellent electrochemical performance. This work underscores the feasibility of high-performance sodium-ion battery anodes derived from biowaste and provides insights into the sodium storage process in biomass-derived hard carbon.

Breaking barriers of CeO2 in energy storage: Hydrothermal energized preparation of mesoporous carbon added CeO2 nanohybrids as supercapacitor electrodes

Inspired by the excellent physio-chemical properties of nano-sized materials, this study details the hydrothermal preparation and electrochemical characterization of mesoporous carbon added CeO2 nanostructures towards the energy storage applications. Cubic CeO2 is observed for the crystal structure and phase of the prepared materials. The formation of nano-sized (∼ 7 nm) quasi spherical-like structure is found from the TEM analysis and it is mainly ascribed to the combined effect of mesoporous carbon and hydrothermal treatment. The charge storage performance of the prepared composites is examined using three-electrode mode. The capacitive behaviour of mesoporous carbon is additionally supported for electrochemical performance in addition to the battery-like behavior of the CeO2 electrodes resulting in an increase of specific capacity by 102.6 %. Hybrid supercapacitor cell is devised and it could yield a specific energy of 31 W h kg–1 (562 W kg–1) and retain 81 % capacity after 3000 continuous charge discharge cycles. With this efficient composite, the future of energy storage may pave the way for more sustainable and powerful energy solutions.

Study of electrochemical behavior of rGO and Metal-Organic Framework nanocomposite electrodes for supercapacitive applications

Abstract This research studied the electrochemical performance of reduced Graphene Oxide (rGO) and a nanocomposite comprising rGO and Metal-Organic Framework-5 (MOF-5) for supercapacitor applications. The nanocomposite, synthesized through a solvothermal method, aimed to capitalize on the synergistic effects of combining rGO with MOF-5 under normal laboratory conditions without utilizing autoclave. By adjusting the concentration of the oxidizing agent, the oxidation degree of rGO was effectively regulated, thereby influencing its structural properties. Utilizing the optimized rGO, electrodes were fabricated for both rGO and MOF5-rGO configurations. Electrochemical studies were carried out using a three-electrode (3E) system with a 6M KOH electrolyte. The MOF-5, reduced graphene oxide (rGO), and MOF5-rGO nanocomposite samples were characterized using X-ray powder diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) to determine their chemical composition and structural information. The Electrochemical Impedance Spectroscopy (EIS) spectra show low internal resistance (Rs) and charge transfer resistance (Rct), indicating higher conductivity of rGO and nanocomposite. The rGO electrode in the 3E system showed a specific capacitance of 65 Fg-1 whereas MOF5-rGO displayed 73 Fg-1 at a current density of 1.2 Ag-1. MOF5-rGO nanocomposite demonstrates better capacitor retention (96%) compared to rGO (90%) at 5A/g. These results indicate that the MOF5-rGO sample is a promising electrode for supercapacitor application.

Effect of Mo on surface reconstruction of FeCoNi-based high entropy alloy film electrode for oxygen evolution reaction

The selection of elements, tune of compounds types and modification of structure are important ways to improve OER activity of high-entropy alloys. The reconstruction behavior of film electrodes during OER process revealed that Mo element has a strong promoting effect on the reconstruction of FeCoNi-based films. It is shown by first-principles that electron-deficient region could be formed near Mo, and electron-rich region could be formed near surrounding elements of Mo. Charge transfer may be the reason that Mo promotes reconstruction of high-entropy alloys. Compared with FeCoNiCr film electrode, FeCoNiCrMo film electrode, the 2p3/2 binding energy peaks of Fe/Co/Ni in which are shifted forward, has more oxygen-containing species and oxygen vacancies. The study also revealed the existence of lattice oxygen mechanism during OER process. The deposition thickness of alloy film has a linear relationship with sputtering time and deposition rate of FeCoNiCrMo. There is an optimal deposition thickness of FeCoNiCrMo film electrode for OER. FeCoNiCrMo film electrodes have the most excellent OER performance: the overpotential is 268 mV, and the Tafel slope is 57.6 mVdec−1.

Impact of compliant electrodes on the dynamics of electromagnetoactive membranes

The dynamics of electromagnetoactive polymer (EMAP) membranes have attracted much attention recently because of their wide range of modern robotic applications. Such applications majorly centered on how the dynamics of this novel class of membranes are affected by the mechanical behavior of the compliant electrode. This article presents the dynamic modeling and analysis of EMAP membranes, examining how the inertia of the electrode, coupled with its inherent viscoelastic properties, impacts its dynamic performance. Both the compression and suspension stages of the membrane are covered here in broad terms. An Euler–Lagrange equation of motion is implemented to deduce the governing dynamic model equation of the membrane system. The findings of the model solutions provide preliminary insights to characterize the dynamic response, instability analysis, periodic behavior, and resonance properties across varying parameters such as inertia, electric field, magnetic field, and prestress. Moreover, the study also evaluates the periodicity and stability of the nonlinear oscillations using Poincaré maps and phase portraits, facilitating an assessment of quasi-periodic to periodic transitions.

Synergistic Enhancements of Zn-ZIF with Nano Zinc Oxide for Hydrogen adsorption, energy storage, and photocatalytic technologies

Creating the porous Zinc-Zeolitic Imidazolate Framework (Zn-ZIF) using a solvothermal technique addresses the need for advanced materials with distinctive properties and cost-effectiveness in modern applications. The PXRD, SEM, UV-DRS, TEM, and TGA/DTG are used to characterize different concentrations of Zn-ZIF. Zn-ZIF's crystalline structure and phase purity have been verified by PXRD. Using diffuse reflectance spectra, the Kubelka-Monk function determined the band gaps of the Zn-ZIF samples, and scanning electron microscopy revealed a more porous structure. At 77 K and 1 bar, the Zn-ZIF solution with a 2:1 ratio had the highest hydrogen storage capacity (1.71 wt%). The electrochemical behavior of several Zn-ZIF electrodes in a 6 M KOH electrolyte was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) experiments. The Zn-ZIF electrode with a 2:1 ratio exhibits a low charge transfer resistance and a high proton diffusion coefficient (D) of 1.687 × 10−4 cm2 s−1. The characteristics of the 2:1 synthesized Zn-ZIF electrode as a supercapacitor were investigated. Our analysis of the generated Zn-ZIF material's specific capacitance values after 2000 cycles revealed an impressive retention rate of nearly 89 %, with values of 296.6 Fg-1. In addition, we examined the photocatalytic activities of the as-synthesized material by exposing it to ultraviolet light and seeing how it degraded organic dyes such as Cango-Red (CR) dye. With a photocatalytic efficacy of 95.06 % for CR dye, Zn-ZIF (2:1 ratio) is the most effective. These findings should provide new knowledge for researchers interested in developing novel Zn-ZIF materials for photocatalytic, energy storage, and hydrogen storage applications.

Simultaneous electro-chemical detection of Pb and Fe by copper-modified carbon paste electrode in the portion of soil

A carbon graphite and copper powder paste electrode (CPE-Cu) was successfully designed as a working electrode for electrochemical analysis. The structural characteristics of this electrode were revealed by X-ray diffraction. Voltammetric techniques and electrochemical impedance spectroscopy were used to assess the electroactivity of the proposed working electrode. X-ray diffraction showed that the composite material has a slightly different crystalline structure to pure graphite, since the copper modification influenced the angles of reflection so that they fluctuated towards slightly larger values. The study of the electrochemical behaviour of the CPE-Cu electrode using cyclic voltammetry showed that the redox phenomena at the electrode surface are almost reversible. Analysis of the soil portion using cyclic voltammetry showed that lead (II) and iron (II) showed current peaks at potentials −0.36 V and +0.12 V respectively. These potentials were confirmed by square-wave voltametry. Cyclic voltammetry and square wave voltammetry showed linearity between the portion of soil in the soil and the electrochemical response. In addition, the study of the effect of the scanning speed showed that the reactions at the working electrode are controlled by a diffusion phenomenon at the surface of the working electrode. Electrochemical impedance spectroscopy showed that the electrode material had a low resistance to charge transfer, with a complete analysis of around 80 ohm.cm2. The heavy metals Cd2+, Pb2+ and Fe2+ were detected simultaneously at trace levels. Calculations of the detection limits for Pb2+ and Fe2+ gave 0.709 ppm and 0.821 ppm respectively. At the end of this work, it can be said that the proposed sensor can be used as an instrument for monitoring the metals studied, as the detection limits were relatively low despite the complexity of the detection medium (portion of soil).

Tuning Deposition Conditions for VN Thin Films Electrodes for Microsupercapacitors: Influence of the Thickness

Vanadium nitride is a highly promising material for micro-pseudocapacitors when used as a bifunctional thin film, i.e. an electrode material and a current collector, owing to its remarkable electrical and electrochemical properties. However, the specific limitations associated with high-rate cycling remain unclear. In this study, we evaluate how the characteristic time associated with charge/discharge of vanadium nitride films is modified with the film thicknesses using electrochemical impedance spectroscopy and cyclic voltammetry measurements coupled to a semi-empirical model commonly utilized to assess the high-rate behaviour of battery electrodes. Both methodologies are in good agreement and revealed that rate capability of this bi-functional material is limited by the VN electrical conductivity. To confirm this finding, VN thin films were sputtered on platinum current collectors, leading to a six-fold reduction in the characteristic time associated with charge/discharge of the current collectors/electrode material. This underscores the importance of using current collectors even for highly conductive electrode materials.

Control and Regulation of Au Hillocks Growth by the Electrical Field and their Metastable Dynamics in Ambient Atmosphere

Abstract With the rapid development of electronic engineering and nanotechnology, the electrical field-induced surface migration plays an increasingly important role in the fields of materials science. By comparing the changes in the surface migration behavior of gold nanogap electrodes under different electric field parameters, we reveal the kinetic processes and influencing factors of electric field-induced surface migration. Under the condition of only 1 pA current limit, under the continuous electric field, the hillcok only appears in the anode and gradually evolve into multiple peaks when rises to some extent. By establishing a finite element model of the nanogap, we find the hillock grows under the field strength gradient. Then hillock growth is biregulated by applying a positive or negative voltage to the drain end of the gap device. Located in the normal temperature atmosphere, the morphology will degenerate, and this feature is opposite to the hillock generated by electromigration.

The Current Shortcomings and Future Possibilities of 3D Printed Electrodes.

3D printing has changed many industries and research areas, and it is poised to do the same for electrochemistry and electroanalytical sciences. The ability to easily shape electrically conductive parts in complex geometries, something very difficult to do using traditional manufacturing techniques, can now be easily accomplished at home, opening the possibility of fabricating electrodes and electrochemical cells with geometries that were once unimaginable. This ability can be a milestone in electrochemistry, allowing the fabrication of systems tailored to specific applications. Unfortunately, this is not what is seen to date, with 3D printing mostly reproducing "traditional" designs, using little of the "freedom of design" promised by the technology. We reason that these results come from too much focus on reproducing the electrochemical behavior of metallic electrodes instead of understanding how material properties impact the performance of 3D printed electrodes and working within these constraints. 3D printing will change electrochemistry and electroanalytical sciences if we understand and learn to work with its limitations.

Building mesoporous channels in lignin-derived microporous carbons to remold the electrochemical behaviors of supercapacitors

The mesoporous structure of the porous carbon electrodes could promote the in-pore diffusion of electrolyte ions. However, the effect of large mesopores with pore sizes larger than 20 nm in the microporous carbons on the diffusion of different electrolyte ions remains unclear. Herein, porous carbon electrodes with mesopores sizes of 23 nm and 40 nm, respectively, are prepared using the ZnO as a hard template. The electrochemical behavior of porous carbon electrodes with large mesopores and microporous carbon electrodes in different sulfate electrolytes are studied and compared. Electrochemical impedance spectroscopy (EIS) tests demonstrate that the wide and short diffusion path provided by large mesopores can reduce the hindrance of multivalent metal cations and SO42−, thus significantly improving the diffusion efficiency of the multivalent metal sulfate cations. Due to the small size and low valence of monovalent metal ions, it is difficult for large mesopores to promote the diffusion of monovalent metal sulfate ions. Therefore, the large mesopores have little impact on the diffusion of monovalent metal ions, whereas they significantly enhance the diffusion of multivalent metal ions.

Unusual electrochemical properties of boron and silicon Co-doped diamond electrodes

Boron-doped diamond (BDD) films exhibit exceptional physicochemical properties and have been utilized in numerous fields. As a common impurity in diamond, silicon is inevitably introduced into the diamond lattice during certain growth process. However, there are limited reports on the impact of silicon co-doping on the electrochemical properties of BDD electrodes. In this paper, we prepared a series of BDD electrodes with various silicon contents and made a systematic evaluation of these electrodes in terms of physicochemical properties. The results indicated that silicon and boron co-doped diamond (SiBDD) electrodes displayed a broader potential window and lower background current compared to the pure BDD electrode. Additionally, we observed that the electron transfer rate of the electrodes in the inner ([Fe(CN)6]3−/4−) redox systems exhibited a rising trend with increasing silicon content, whereas the electron transfer rate of the outer ([Ru(NH3)6]3+/2+) redox systems displayed contrasting trend. Surface analyses and electrochemical measurements results suggested that the unusual phenomena might stem from the alterations in surface functional groups and carrier density of the electrode inducing by silicon co-doping. In general, our results demonstrate, for the first time, that Si co-doping can influence the surface functional groups and carrier behavior of BDD electrodes, thereby altering the electrode's electrochemical performance. This provides new insights for the design of high-performance diamond electrodes.

Unraveling the Intrinsic Thermal Behavior of Freestanding Ionomer Films Depending on Thickness from Commercial Membrane to Nanofilm.

Proton exchange membrane fuel cells (PEMFCs) for automotive applications are required to achieve mechanical reliability at various temperatures ranging from subfreezing to 80 °C. The thermal behavior of the electrode should be considered at the initial design stage to design a robust automotive fuel cell electrode. Recently, a behavior different from that of the bulk state has been reported for ionomers with a few nanometers of thickness. Therefore, the intrinsic thermal behavior of ionomer films with thicknesses from micrometers to nanometers is quantitatively investigated in this study. By introducing the fabrication of a pseudo-freestanding Nafion thin film and in-plane thermal strain measurement method on the water surface, the thermal expansion of the freestanding Nafion thin film was successfully measured with minimizing substrate constraints. Thermal strain measurement and X-ray scattering studies revealed that the weakening of intermolecular interaction within the hydrophobic and hydrophilic domains in the Nafion thin film caused thermal expansion, and well-structured hydrophobic domains could suppress thermal expansion. The thermal expansion behavior with different heat treatments provides evidence of the thin-film-to-bulk transition of the fully hydrated Nafion film. Intrinsic thermal behavior without substrate interactions can facilitate an understanding of the thermal behavior of electrodes and provide insight into designing a robust PEMFC in temperature-varying environments.

Behavior of Polymer Electrode PEDOT:PSS/Graphene on Flexible Substrate for Wearable Biosensor at Different Loading Modes.

In recent years, flexible and wearable biosensor technologies have gained significant attention due to their potential to revolutionize healthcare monitoring. Among the various components involved in these biosensors, the electrode material plays a crucial role in ensuring accurate and reliable detection. In this regard, polymer electrodes, such as Poly(3,4 ethylenedioxythiophene): poly(styrenesulfonate), combined with graphene (PEDOT:PSS/graphene), have emerged as promising candidates due to their unique mechanical properties and excellent electrical conductivity. Understanding the mechanical behavior of these polymer electrodes on flexible substrates is essential to ensure the stability and durability of wearable biosensors. In this paper, PEDOT:PSS/graphene composite was spray-coated on flexible substrates at different growth conditions to explore the effect of the deposition parameters and mode of mechanical loading (longitudinal or transversal) on the electrical and mechanical behavior of the fabricated samples. It was found that the coating grown at lower temperatures and higher spraying pressure exhibited stable behavior no matter the applied stress type.

Diazonium-Functionalized Silicon Hybrid Photoelectrodes: Film Thickness and Composition Effects on Photoelectrochemical Behavior.

Aryl diazonium electrografting is a powerful method for imparting molecular functionality onto various substrates by forming a stable carbon-surface covalent bond. While the high reactivity of the aryl radical intermediate makes this method fast and reliable, it can also lead to the formation of an insulating and disordered multilayer film. These thick films affect electrochemical performance, especially for semiconductor substrates used in photoelectrochemical applications. We studied the effects of film thickness and composition by electrografting in situ-generated aminobenzene diazonium salts onto both n-type and p-type silicon electrodes at fixed potentials. Next, we attached ferrocene to the amine-terminated films and probed their (photo)electrochemical behavior. Cyclic voltammetry measurements showed decreased electrochemical reversibility with increasing diazonium film thickness; this reversibility was restored when ferrocene was incorporated throughout the film with a layer-by-layer deposition process. Finally, we compared the behavior of dark p-type electrodes to n-type photoelectrodes and observed differences in the electrochemical reversibility that we attribute to the change in potential drop across the two interfaces.